Several conveyor belt arrangements are currently in use for transporting food or other products through freezers typically including an insulated enclosure for maintaining temperatures which are below ambient temperature. In order to provide a relatively long path length within an insulated enclosure of minimal volume and external surface area, a conveyor belt which transports products through the enclosure is frequently made to traverse one or more helical paths (which are sometimes termed "spiral" paths in the industry). Such conveyor belts experience a change in configuration across their width, generally along both their inner and outer edges, at points of transition between a straight-line path section and a helical path section. To date, such conveyor belts either have undergone a contraction along their inner edge alone or have undergone contraction and expansion along their inner and outer edges, respectively, in assuming a helical path configuration.
Such conveyor belts are generally driven, in part, by frictional engagement with a central drum which rotates about a vertical axis, and it accordingly becomes necessary to attempt to "overdrive" such belts to maintain sufficient tension in the belt to achieve the needed frictional engagement in the helical region. This becomes increasingly difficult to maintain when there is more than one helical section through which the belt passes within the freezer enclosure. Moreover, when the inner edge region of such a conveyor belt undergoes contraction, the distances between the radially inner ends of rods or other transverse members of the conveyor belt change individually and are not uniform. Although attempts have been made to positively drive such conveyor belts by engagement with the exterior surface of such a rotating drum, as for instance shown in U.S. Pat. No. 4,741,430 (May 3, 1988), they have not been successful because of the creation of excessive wear in the vertical driving elements and in the belts, which has often caused upsetting of the belt (Christmas-tree effect) as a result of high tension at the outward edge of the belt which creates hoop stress and eventual damage to the conveyor belt.